The present invention is generally directed to magnetic transducers of the type that are used to transfer information between a signal generation or utilization device and a magnetic storage medium, such as a magnetic tape-or disk. More particularly, the present invention is directed to a solid state scanning transducer in which portions of the transducer are selectively activated to record and/or reproduce information along different portions of the storage medium.
Generally speaking, a magnetic transducer of the type to which the present invention pertains typically comprises a core of high permeability magnetic material that is provided with a non-magnetic gap between two magnetic poles. This gap interrupts the path of flux flowing within the core to cause the flux to fringe from the core at the gap. In a conventional transducer, this fringing flux is directly coupled into the magnetic storage medium. Varying or modulating the magnitude and/or polarity of the flux in accordance with information of interest orients the direction of magnetic dipoles in the magnetic storage medium, thereby recording the information. Thereafter, flux which is produced by the dipoles is coupled to flow in the flux path defined by the core, and be detected by an appropriately positioned winding to reproduce the recorded information. This flux, which is modulated in accordance with the information of interest, is referred to as "signal flux."
In a conventional magnetic transducer, the coupling of signal flux between the storage medium and the transducer takes place across the entire width of the transducer. In this context, the "width" of the transducer is defined as the dimension that is parallel to the interface between the core and the medium, and orthogonal to the direction of flux flow around the magnetic core and across the gap. During the recording of time varying information on the storage medium, the storage medium and the transducer are moved relative to one another. This relative motion is effected in various ways leading to a number of different recording formats. In one format, a storage medium such as a tape is transported past the transducer in a longitudinal direction perpendicular to the width of the transducer. In this format, the information is recorded on the tape in a track which is coextensive with the length of the tape.
In an effort to increase the amount of information recorded on a tape, it has been known to move the transducer mechanically at a high speed relative to the tape, to scan its gap across the width of the tape. In devices recording information in this fashion, the width of the transducer is much less than that of the tape, and the transducer is moved across the tape in a direction that is transverse to the longitudinal direction in which the tape is transported.
For example, in some transducing arrangements the transducer is mounted on a drum that rotates about an axis generally parallel to the direction of tape transport. As a result of this movement, the transducer defines a track which is substantially perpendicular to the longitudinal dimension of the tape. Repeated scanning of the transducer in this manner, coupled with the transport of the tape in its longitudinal direction, produces discrete parallel tracks that extend across the width of the tape and are successively spaced along the length of the tape.
While the transverse scanning of the transducer significantly increases the amount of information stored on a tape, it will be appreciated that the high relative speed of the transducer, coupled with contact between the tape and the transducer, also increases the amount of wear to which the tape and the transducer are subjected. In an effort to minimize this wear, solid state scanning transducers have been developed. In place of mechanical movement of the transducer, solid state transducers utilize magnetic and/or electronic means to selectively control the location of a limited portion of the transducer through which the signal flux is transferred between the transducer and the medium. In some known arrangements, this limited portion is defined by a control flux that selectively saturates portions of the transducer while leaving adjacent portions unsaturated. The signal flux only flows in the unsaturated portions of the transducer, and thus is confined to a limited area. In the context of the present invention, this limited area of the transducer, through which flux is coupled between the transducer and the recording medium, is referred to as a "signal transfer region". By varying the control flux to vary the location of the saturated portions along the width of the transducer, the signal transfer region is scanned across the transducer. Different types of solid state scanning transducers which operate in this manner are disclosed, for example, in U.S. Pat. Nos. 3,391,254, 3,435,440, 3,555,204 and 4,322,763.
As illustrated by these exemplary patents, the control flux can be employed in different manners to effect the scanning of the signal transfer region. In another type of solid state scanning transducer, different from those described in these exemplary patents, the signal transfer region is defined in a gap-less magnetically permeable body of material that is distinct from the magnetic core itself. The present invention is concerned with this latter type of transducer. In this particular type of solid state scanning transducer, the control flux established in the magnetic core is coupled by a non-magnetic gap into the distinct body of magnetic material located magnetically proximate the recording medium and the core. This body of material bridges the gap of the core, and is referred to herein as a "keeper". The keeper defines a path for the flux which leaves the core as a result of its non-magnetic gap. To effect scanning of the signal transfer region, the control flux is generated with a gradient along the width of the gap. At the locations of higher flux density, the control flux can be sufficient to selectively saturate portions of the keeper material. The selective saturation of the keeper material effectively limits the regions within which the signal flux can flow between the transducer and the keeper body.
To effect recording of the information in this type of transducer, the signal flux flowing within the keeper is coupled from the face of the keeper into the magnetic recording medium. During playback, only that flux which emanates from the recording medium and enters the keeper in the confined area of the signal transfer region is detected by the signal winding.
Thus, rather than the entire width of the transducer being used to record and/or reproduce information, only a limited portion of its width is employed to record or reproduce information at any one instant. By varying the gradient of the control flux along the width of the transducer, the location of the signal transfer region of the keeper is varied. In this manner, the location at which the signal flux is coupled between the transducer and record medium is electronically and/or magnetically scanned along the width of the transducer to thereby cause different locations along the non-magnetic gap to effect transfers of information with respect to the record medium.
Further information pertaining to this type of transducer can be found in copending U.S. Pat. Application Ser. No. 085,676, corresponding to International Application Publication No. WO 87/03729, published on Jun. 18, 1987, the disclosure of which is incorporated herein by reference thereto. This type of magnetic transducing arrangement provides a number of advantages in the use of a solid state scanning transducer, and it is desirable to improve upon that arrangement. In one aspect, it is desirable to provide a solid state scanning transducer which does not rely upon magnetic saturation to effect the scanning of the signal transfer zone through which the signal flux flows. A scanning transducer which does not utilize magnetic saturation can operate with lower fluxes and therefore the power requirements of the transducer will be less. Furthermore, by using lower amounts of flux to define the signal transfer region, the sensitivity of the transducer is increased, since there is a smaller likelihood that low level and short wavelength information signals will be swamped out or demagnetized by the high control flux that may be required to produce saturation.
In another aspect, it is desirable to provide separate paths for the control flux and the signal flux, preferably in separate structures such that these fluxes only cross paths in the area of the signal transfer region of the keeper. By keeping these two types of flux separate from one another, interference between them is minimized, thereby further increasing the sensitivity of the transducer.